Stairway construction



Sept. 16, 1969 Filed March 20. 1967 F. B. SMITH ET AL 3,467,220

swunwu cons'rnuc'rxou 2 Sheets-Sheet 1 l l I an" INVENTORS FRANK BURCHARD SMITH STEPHEN BRIAN HARLEY m M QM: i rye.

ATTORNEYS Sept. 16, 1969 F. B. SMITH ET Filed March 20. 1967 STAIRWAY CONSTRUCTION 2 Sheets-Sheet 2 F I G. 8

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INVENTORS FRANK BURCHARD SMITH BYSTEPHEN BRIAN HARLEY m M Mafia/ ATTORNEYS United States Patent STAIRWAY CONSTRUCTION Frank Burchard Smith, 1737 Solano Ave., and Stephen Brian Harley, 1993 El Dorado St., both of Berkeley, Calif. 94707 Filed Mar. 20, 1967, Ser. No. 624,597 Int. Cl. E04f 11/12 US. Cl. 182115 25 Claims ABSTRACT OF THE DISCLOSURE An improved open-riser stairway comprises an integrated system of standard stairway components made of lightweight anodized aluminum stampings and extrusions. The stairway includes a single hollow flanged stringer and hollow, Wedge-shaped steps. The steps are readily secured at their centers to the stringer flanges by means of rivets. An open network of these stringers form the framing for the stairway landing, and the deck thereof consists of matched interlocking panels riveted to the stringers. The tread surfaces of the stairs and landing are treated to resist accumulation of ice and snow thereon. Also, for this reason electric heating elements are included inside the steps and panels and connected by conductors in the stringers to a current source. The stairway also has a railing which may be anchored to the panels and to reinforcing inserts in the steps by means of rivets.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to an improved stairway construction and to various components thereof and accessories therefor. More particularly, it relates to a lightweight, metallic, open-riser type of stairway that is readily assembled on the job site by one or two men without the use of heavy equipment and without the need of heavy or elaborate tools or skilled labor.

The invention is directed primarily to the market for open-riser stairways. This style presents a pleasing, uncluttered, airy appearance that is highly desirable in many indoor and outdoor applications. This effect is generally enhanced by the use of only a single stringer supporting all of the steps at their centers.

Description of the prior art Prior to the present invention, stairways of this type have generally been made of concrete, which has the advantages of being durable and attractive, while at the same time providing a sturdy construction even though the steps are supported at their centers rather than at their ends.

They do, however, have several drawbacks. First, frequently the steps do not fit properly and they sometimes stain and crack. These problems are often aggravated by the fact that the concrete steps and associated stairway components are usually manufactured in small shops that lack suflicient technical services for the maintenance of optimum quality in the finished product.

Also, the conventional stairways are quite costly to install. This stems from the fact that the individual concrete steps are rather heavy, weighing typically as much as 125 lbs. each. Consequently, each hefty concrete step generally requires three construction personnel for its installation: two laborers to hold the step in place and a welder to weld anchor plates in the step to the stringer to secure the step to the stringer. Further, the fitting of a railing to concrete steps is generally a time-consuming task. To this must be added the cost of running the welding equipment, as well as the expense due to accidents Patented Sept. 16, 1969 resulting from handling the unwieldy steps. Moreover, any departure from the stock construction, such as providing a non-standard stairway slope requires steps which are made to order and is unduly costly.

Additionally, the heavy weight of the concrete stairway, as contrasted with a wood construction, for example, means that stronger and more expensive structural supports must be included in the building, particularly if a multiple-story stairway is to be constructed.

SUMMARY OF THE INVENTION Accordingly, a principal object of this invention is to provide an improved stairway construction suitable for either indoor or outdoor installation and capable of erection with a minimum amount of labor.

A further object of the invention is to provide a stairway construction of the above type which is light in weight and therefore does not require massive supporting elernents.

Another object of the invention is to provide a stairway construction of the above type which has a pleasing appearance and so is suitable for indoor usage.

A more particular object of the invention is to provide a stairway of the open-riser type in which the individual steps are supported on a single stringer.

A further object of the invention is to provide a stairway construction which is strong and sturdy and yet which is relatively inexpensive to make and install in place.

Another object of the invention is to provide a construction of the above type which can be efiiciently heated to prevent the accumulation of ice and snow thereon.

Yet another object of the invention is to provide variout lightweight stairway components, such as steps, stringers, landings and railings for a stairway having the foregoing characteristics.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.

Briefly, our stairway construction comprises an integrated system of standard stairway components made of lightweight anodized aluminum stampings and extrusions. The stairway employs a single hollow flanged stringer which extends up to a landing and supports a flight of steps. The steps themselves each comprise a pair of metal stampings which mate to form an enclosed, structurallysturdy shell. The steps are anchored near their centers to the stringer flanges which shorten the lever arm between the end of the step where weight is applied and the points of securement of the step to the stringer. At the same time, the flanged construction widens the support base for the step by allowing the aforementioned points of securement to be farther part than would be possible with a nonflanged stringer. Also, each step has a truss-like configuration which reinforces the step.

By virtue of the aforementioned stress-relieving step and stringer shapes, ordinary hollow rivets of the type sold by United Shoe Machinery Company under its trademark Pop Rivet may be employed to anchor the steps to the stringer. In the event that the flight of stairs is to have a nonstandard slope, the identical step may be used in conjunction with a pitch plate secured between the step and the stringer to tilt the step so that its tread surface is horizontal. Additional such stringers arranged in an open network form the framing for the stairway landing. Matched interlocking panels made of hollow lightweight aluminum extrusions overlie the framing. These are also anchored in place by means of rivets.

The stairway may also include a railing extending up the flight of stairs and around the landing. In this event, selected steps are specially reinforced to provide a secure base in which to anchor the railing.

The fact that the entire stairway is made of aluminum gives it several important advantages over its conventional counterpart. First, the stairway components and, in fact the entire stairway are lightweight. This means that the stairway can be assembled, if need be, by a single individual quickly and economically with minimum chance of injury. Moreover, the stairway does not add materially to the overall load on the structural elements of the building in which it is installed. Second, aluminum is a relatively inexpensive material which can be formed to a variety of shapes and designs on a mass production basis so that the quality of the finished product can be carefully controlled. Third, the properties of aluminum make it receptive to anodic coating for scratch resistance, and it is easily embossed, coated and prepainted. Thus, for only a small additional material cost, the aluminum stairway components can be decorated and treated in a variety of different ways to make it very attractive; attractive enough, in fact, to compete with the more conventional decorative stairway materials such as marble, polished wood and stone. Fourth, the anodized aluminum parts are resistant to the accumulation of ice and snow, thereby reducing the possibility of a serious accident. Also, the excellent heat transfer qualities of anodized aluminum allow it to be economically heated. This permits the elimination of the arduous task of manually removing ice and snow from frozen steps. Fifth, the aluminum stairway saves maintenance costs by not cracking, rusting, or waterstaining as will its concrete counterpart. This gives the present stairway a unique advantage over conventional exterior stairways.

In short, the present stairway is not only extremely functional, inexpensive to make and easily installed using a minimum of labor and supervision, it is also quite attractive so that it can be used inside as well as outside most structures.

DESCRIPTION OF THE DRAWINGS For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is a perspective view of a stairway embodying the invention;

FIG. 2 is a front view partly broken away, of a step used in the stairway of FIG. 1;

FIG. 3 is a bottom view of the step;

FIG. 4 is a vertical section taken along the line of 44 of FIG. 3;

FIG. 5 is an enlarged fragmentary section of the step taken along line 55 of FIG. 3;

FIG. 6 is a fragmentary perspective view with parts cut away of the stairway stringer;

FIG. 7 is a fragmentary side view of the stringer showing the manner in which it is connected to the stairway landing at the upper end;

FIG. 8 is a view along line 8-8 of FIG. 7 showing the manner in which the steps are attached thereto;

FIG. 9 is a cross section of part of the landing; and

FIG. 10 is an enlarged fragmentary cross section of the stringer and an attached step showing the manner in which the electrical connections to a heating element in the step are preferably made.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 of the drawings, the present stairway comprises a stair flight indicated generally at 10 leading up to a landing 12 which extends out from a building wall 13. The flight of stairs includes several individual steps 14 supported at their centers by a single stringer 16 secured between the ground and landing 12. Similar stringers 17 also form the framing for landing 12. These are supported by conventional posts 18. The deck of landing 12 comprises a series of matched interlocking panels 19 anchored to stringers 17. A railing 20 is supported by posts 22 anchored firmly to panels 19 and selected steps 14.

All of the aforementioned stairway components are constructed of lightweight aluminum extrusions and stampings which give it the unique advantages noted above, some of which will be dealt with in greater detail later.

Referring now to FIGS. 2-4, each step 14 is a shell made up of mating upper and lower anodized aluminum sections 30 and 32 respectively. The two sections are press-fit together, forming a wedge-shaped enclosure whose longitudinal medial cross section is, in essence, a trapezoid, and whose transverse medial cross section is a triangle.

More particularly, the lower step section 32 is generally rectangular, but it is also downwardly dished. It has an upright rectangular edge margin 34, converging triangular side walls 36 and trapezoidal front and rear walls 38 and 40 respectively. The slope of rear wall 40, i.e. the acute angle included between the extended planes of wall 40 and the top 14a of the step (FIG. 4), is the same as the slope of stringer 16, i.e. the acute angle between ground and stringer 16, when stair flight 10 has a standard slope in its ascent to landing 12 (FIG. 1). Thus, when the steps 14 are secured to stringers, their tops 14a are generally horizontal. While it is contemplated that the present flight of stairs will usually have a standard slope, provision is made for adjusting the tilt of steps 14 relative to stringer 16 for custom-made installations as will be described later.

The slope of front wall 38 is chosen to keep the wall out of the way and to give the stairway as a whole a pleasing overall appearance. Thus, in the illustrated embodiment of our invention, the front wall 38 of each step is wider than wall 40, and its slope is somewhat less than that of wall 40.

The upper step section 30 constitutes a tight cover over the lower half. The step top 14a constituting the top wall of section 30 is generally rectangular, but it has a slight camber (FIG. 4) to lend added structural integrity to the step and for drainage. Also, a tread design 42 (FIG. 2) may be stamped therein. A skirt 44 bends downward from step top 14a and engages tightly over edge margin 34 in lower section 38. The two coupled together sections make a strong enclosed box-like structure which resists bending and twisting.

As best seen in FIGS. 14, the inclined walls 36, 38 and 40 of step 14 constitute rigid struts between the points of securement of the step and stringer 16 and the edges of the step. Consequently, they firmly support and reinforce the step particularly at the ends and front of the step top 14a.

The step construction just described is not only utilitarian, but also, when joined to stringer 16, yields an open-riser stairway, which is aesthetically appealing and particularly pleasing to the eye. Consequently, it has farreaching application in the interiors of offices, apartments and other buildings.

Referring now to FIGS. 3-5, when the present stairway is used exteriorly, a heating element 50 is preferably bonded to the inside of each stop top 14a. Heating element 50 connects with a plug 52 protruding from wall 40. The plug is, in turn, coupled to electrical conductors in stringer 16 when the step is secured thereto as will be described later. Preferably also, an insulating fill 54 (FIG. 5) such as a nonflammable, non-absorbent foam scrap is placed in each step 14 below heating element 50 prior to assembling the step. This minimizes heat loss through the bottom of step 14. In addition, it damps metallic ringing sounds due to the box-like construction of the metal step and gives the step the sound of a solid, sturdy structure.

The fact that the step is anodized increases its heat transfer capabilities drastically. Typically, it may improve by as much as 40% over an equivalent nonanodized member. Moreover, the physical properties of the anodic coating itself make it resistant not only to scratches, but also to the accummulation of ice. The latter property can be enhanced even more by impregnating the anodic coating with glycerine or graphite. All of these factors maximize the heating effect of element 50 so that it can consist of a simple electrical tape which consumes relatively little power.

Referring particularly to FIGS. 1 and 5, those of steps 14 supporting railing 20 are reinforced to provide very secure anchoring points for the posts 22. More particularly, a generally triangular reinforcing member 56 in the form of a hollow aluminum extrustion is seated inside each of these steps below post 22. The cross section of reinforcing member 56 has the general shape of a right triangle and is dimensioned to fit so that its longer leg 56a engages the top 14a of step 14 and its shorter leg 56b engages edge margin 34. Member 56 is held in place by means of ordinary hollow rivets 57 applied at the end of the step through its margin 34 and skirt 44. Other rivets 57 are installed, in like manner, through the opposite end of step 14 so that sections 30 and 32 are held together permanently. The actual securement of railing 20 to the steps will be described later.

Referring now to FIGS. 6 and 8, the stringer 16 (as well as stringers 17, FIG. 1) comprises a hollow extruded aluminum box girder 60 having integral, oppositely extending flanges 62 adjacent to its top wall 60a. A pair of electrical busses 64 and 66 are mounted inside box girder 60 for supplying current to the heating elements 50 in steps 14. Busses 64 and 66 consist of a pair of spaced parallel conductors mounted in and projecting up from an insulating fixture 68 extending along through the stringer. Fixture 68 is secured to top wall 60a by a series of countersunk screws 70 (FIG. 6) screwed through wall 60a into a longitudinal rib 68a which extends up between busses 64 and 66.

A series of plug openings 72 are formed in top wall 60a of stringer 16 at points therealong where steps 14 are secured (FIG. 1). These openings are shaped to receive plugs 52 when the steps 14 are anchored to the stringer.

Referring particularly to FIG. 8, when installing the stairway, each step 14 is positioned transversely on stringer 16 so that its plug 52 extends through the corresponding plug opening 72 in the stringer and makes electrical contact with busses 64 and 66. The step 14 is then anchored to the stringer by means of hollow rivets 78 inserted into holes 73 extending through the stringer flanges 62 (FIG. 6), and thence into registering holes 74 (FIGS. 3 and 4) in rear wall 40 of step 14. Thus, no rivet holes are required in box girder 60 through which water could leak and short circuit the busses 64 and 66.

The flanges 62 give the stringer a T-shaped configuration which greatly strengthens and reinforces the flight of stairs 10, particularly at the points of securement of steps 14 to the stringer.

More particularly, flanges 62 lend a considerable amount of sideways stiffening to stringer 16. While the same strengthening might be accomplished by enlarging box girder '60, this would add considerable bulk and mass to the stringer and tend to spoil the appearance of the stairway. Moreover, rivets 78 could not be installed into steps 14 from below the stringer. Rather, the bottom step sections 32 would first have to be attached to the stringer, and then the steps would have to be assembled at the site. While this can be done with the present construction, it increases installation costs.

Also, flanges 62 constitute load bearing members which shorten the lever arm (i.e. the length) between rivets 78 and the end of the step on which weight is placed. At the same time, however, these flanges 62 increase the lever arm between these rivets 78 and the remaining rivets 78 on the opposite side of the stringer 16 which exert the downward force on the step opposing the aforesaid weight. This feature greatly minimizes the stresses on steps 14 in the region of rivets 78 to the extent that ordinary, inexpensive hollow rivets 78 can be used to anchor the steps. These are installed through flanges 62 quickly and easily from below stringer 16 without any elaborate equipment. Moreover, this assembly can be accomplished by one man because the steps themselves are lightweight and easy to handle. Each step 14 is automatically properly positioned on the stringer when its plug 52 is received in corresponding plug opening 72. The installer need then only align the rivet holes 73 and 74 and insert rivets 78 through these holes.

Generally, the flight of stairs .10 will have a standard slope. In this event, steps 14 are secured directly to stringer 16 as described above. If, on the other hand, a nonstandard slope is desired, then a lightweight extruded aluminum shim or pitch plate 79 (FIGS. 7 and 8) is placed between each step 14 and the stringer 16 prior to attaching the step. The wedge angle on the shim 79 is such that it tilts step 14 so that step top 14a is substantially horizontal when the stringer 16 is in place as seen in FIG. 1. Of course, the shim 79 has a plug opening 80 and rivet holes 81 (FIG. 8) in register with the corresponding opening and rivet holes in stringer 16.

Referring now to FIGS. 1 and 7, stringer 16 is suspended from landing 12 by means of an extruded aluminum right-angle bracket 82 whose lower end 82a may be mitered to correspond generally with the slope of stringer 16. The bracket 82 is attached to the upper end of stringer 16 and the back of frame 17 at the front of the landing 12 by means of threaded nuts and bolts 83 and 84 respectively extending through suitable holes drilled through those elements. As the entire flight of stairs 10 weighs relatively little, all the steps 14 can be anchored to stringer 16 as aforesaid, and the whole assembly lifted up and secured quickly and easily to the landing 12 by one, or at most, two men.

As seen in FIGS. 1, 7 and 9, frame member 17 supporting panels 19 are essentially the same as the stringer 16 described above. They are bolted together and to upright posts 18 in the usual fashion. Panels 19 comprise hollow extruded aluminum matched modules having a nonslip tread 42. The panels interlock along mating edges 19b and 190 respectively and they are interchangeable, except for the panel 19 edge 19d (FIGS. 7 and 9) facing the flight of stairs 10 which should be vertical. The panels 19 may be of any desirable length commensurate with the size of landing 12 and their number may be increased to make a full sun deck. They are supported as needed by an open network of stringers 17 strategically placed below the panels.

Panels 19 have an anodic coating much like that applied to steps 14. Accordingly, their surfaces are scratchresistant and ice-resistant exactly as described above in connection with steps 14. Also, like steps 14, the panels 19 may contain heating elements 50 and insulation 54 to give the panels the same desirable characteristics noted above. And, in like manner, heating elements 50 in the various panels are plugged into their supporting stringers 17.

Referring now to FIGS. 1 and 5, the posts 22 supporting railing 20 fit into flanged sockets 85 anchored firmly to panels 19 and to those of steps 14 containing reinforcing members 56. The securement of each socket 85 to the corresponding reinforcing member 56 within a step 14 is accomplished quickly and inexpensively by inserting rivets 86 through holes drilled through the flange of socket 85 and through leg 56a of member 56. (A modified socket 85 may be anchored to leg 56b by rivets 57). Since member 56 is hollow, hollow rivets.

can be employed for this purpose. The legs 56a and 56b of member 56 have sufiicient thickness to anchor most railing systems that tie into either the top and/ or side of the step. The above-described supporting railing structure is light in weight and will not work loose. Moreover, it can be installed more quickly and cheaply and will last longer than many railing systems used in conventional open-riser stairways.

Referring now to FIG. 10, the plug 52 in each step 14 (and panels 19) is a generally cylindrical insulating member supporting a pair of clip-like terminals 90 and 92 which resiliently engage over busses 64 and 66 in stringer 16 (and stringers 17), making good electrical contact therewith. The leads of the heater element 50 are soldered to these terminals. Plug 52 has a reduced diameter neck 94 received in a slightly larger opening 96 in step wall 40. Neck 94 is itself circumferentially grooved at 98. A resilient C-shaped clip 100 is snapped in place in groove 98 within step 14 to anchor the plug firmly to wall 40.

Preferably also a gasket 102 seats in groove 98 to exclude moisture from the interior of step 14. Also, if needed, another gasket 106 may be included in the countersunk opening 72 in wall 60a to ensure that moisture does not enter box girder 60 and short circuit busses 64 and 66 therein.

Electrical connections (not shown) between the various stringers 16 and 17 (FIG. 1) are then made in a conventional way with leads (not shown) from a power source.

As seen from the foregoing, we have devised a stairway comprising an integrated system of lightweight components made of aluminum. These components can be mass-produced with precision in the factory, and then installed quickly and easily by a single relatively unskilled person. Accordingly, manufacturing and installation costs associated with the present stairway are unusually low. Moreover, the use of anodized aluminum for the stairway components gives them a scratchand mar-resistant finish and also minimizes the accumulation of ice and snow thereon. The anodic coating also greatly increases the efliciency of the heating system incorporated into the stairway when weather conditions demand it. Finally, the configuration of the steps and stringers makes for an unusually strong and sturdy stairway structure of the open-riser type. And, while the stairway is extremely functional, it also presents an unusually good appearance so that it can be used inside as well as outside apartments, offices and other buildings.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efliciently attained and, since certain changes may be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Having described our invention, what we claim as new and desire to secure by Letters Patent is:

1. An improved stairway construction comprising (A) an elongated hollow tube (16) for connection to a stairway landing (12), said tube having a pair of opposite side extending flanges;

(B) one or more shell-like steps (14) arranged crosswise on said tube, each said step having a tread surface (14a); and

(C) means (78) for anchoring each of said steps only to said tube flanges.

2. An improved stairway construction as defined in claim 1 wherein each said step includes (A) a downwardly-dished bottom portion (32), said bottom portion having a flat rear wall (40) engaging said tube, and

(B) a cover (30), said cover (1) engaging over said bottom portion, and (2) making an acute included angle with said rear wall.

3. An improved stairway construction as defined in claim 2 and further including a pitch plate (79) secured between said rear wall and said tube for altering the tilt of said tread surface relative to said tube.

4. An improved stairway construction as defined in claim 1 (A) and further including a landing 12), said landing comprising (1) beams (17) secured together to form a framing network; and (2) one or more matched panels (19) overlying said network; and (B) wherein an end of said first-mentioned tube (16) is secured to said landing so that each said tread surface is substantially horizontal.

5. An improved stairway construction as defined in claim 4 wherein said beams are flanged tubes.

6. An improved stairway construction as defined in claim 4 and further including (A) heating elements (50) inside each of said panels;

and

(B) means (52) for electrically connecting said elements to a power source.

7. An improved stairway construction as defined in claim 4 and further including a railing (20, 22) anchored to said landing and at least one of said steps.

8. An integrated open-riser stairway comprising (A) an elongated tube (16) having a pair of opposite side extending flanges (62) adjacent a surface (60a) thereof;

(B) means defining spaced openings (72) in said surface;

(C) a pair of insulated electrical conductors (64, 66)

extending along inside said tube;

(D) a step comprising (1) a hollow shell (14) having (a) afiat top wall (14a); and (b) a flat rear wall (40) making an acute angle with said top wall; (2) an electrical heating element (50) fastened inside said top wall; (3) a connector (52) connected to said element and protruding from said shell; and (4) thermal insulating material (54) inside said shell below said element;

(E) said step being positioned so that (1) said rear wall engages said surfaces; and

(2) said connector extends through one of said openings and electrically connects to said pair of conductors; and

(F) a set of fasteners (78) extending through said flanges and into said rear wall for anchoring said step to said tube.

9. An integrated open-riser stairway as defined in claim 8 wherein (A) said conductors comprise a pair of spaced electrical busses protruding up toward said openings; and

(B) said connector comprises an electrical plug secured in said rear wall, said plug having a pair of contacts (90, 92)

(1) electrically connected to said heating element;

and (2) resiliently engaging said busses. 10. An integrated open-riser stairway comprising (A) an elongated hollow tube (16) having opposite side extending flanges (62) adjacent one surface (60a) thereof; and

(B) one or more shell-like steps (14), each step comprising (1) a relatively flat top portion (30); and (2) a dished bottom portion (32), said bottom portion having (a) a relatively flat rear wall (40) engaging said tube surface;

(b) a pair of opposite end walls (3'6) splaying out from said flanges to the ends of said top portion; and

(c) fasteners (78) extending through said flanges and each said rear wall for anchoring said steps to said tube, said flanges shortening the lever arm between said fastenings and the end of said step on which weight is applied, while lengthening the lever arm between said fastenings and the forces opposing said weight, thereby minimizing the stresses on said fastenings.

11. An integrated open-riser stairway as defined in claim and further including (A) a landing (12); and

(B) means (82) for securing one end of said stringer to said landing so that each said top portion is substantially horizontal.

12. An integrated open-riser stairway as defined in claim 11 wherein said landing comprises (A) an open horizontal network of flanged tubes (17) and (B) one or more panels (19) permanently positioned on said network, each of said panels (1) consisting of a hollow extrusion, and (2) having mating edges (19b, 19c) interlocking with adjacent panels.

13. An integrated open-riser stairway as defined in claim 12 wherein the load bearing elements of said stairway are made of aluminum.

14. An stairway stringer comprising (A) an elongated tube (16) having a pair of opposite side extending flanges (62) adjacent a surface (60a) thereof;

(B) means defining spaced openings (72) in said surface; and

(C) a pair of insulated electrical conductors (64, 66) extending through said tube opposite said openings.

15. An improved stairway construction comprising (A) an elongated tube (16) for connection to a stairway landing (12), said tube having a pair of opposite side extending flanges (62);

(B) one or more shell-like steps (14) arranged crosswise on said tube, each said step having a tread surface (14a);

(C) rivets (78) for anchoring each of said steps to said tube flanges;

(D) a heating element (50) in each said step below said surface;

(E) a pair of electrical conductors (64, 66) extending through said tube; and

(F) means (52) for electrically connecting each said heating element to said conductors.

16. An improved stairway construction as defined in claim 15 and further including heat insulating material (54) contained inside each said step below said heating element.

17. An improved stairway construction comprising (A) an elongated tube (16) for connection to a stairway landing (12);

(B) one or more shell-like steps (14) arranged crosswise on said tube, each said step having (1) a downwardly dished bottom portion (32); said bottom portion having a flat rear wall (40) engaging said tube; and

(2) a cover (30), said cover (a) engaging over said bottom portion;

(b) making an acute included angle with said rear wall;

(c) means (78) for anchoring each of said steps to said tube;

(d) a hollow reinforcing member (56) positioned inside at least one of said steps at one end thereof;

(e) railing supporting means positioned at said end of said step adjacent said reinforcing member; and

(f) means (86) for securing said railing supporting means through said one step to said reinforcing member.

18. An improved stairway construction comprising (A) an elongated tube (16) for connection to a stairway landing (12);

(B) one or more shell-like steps (14) arranged crosswise on said tube, each said step having an anodized aluminum tread surface (14a) impregnated with glycerine;

(C) means (78) for anchoring each of said steps to said tube;

(D) a landing (12), said landing comprising (1) beams (17 secured together to form a framing network; and

(2) one or more matched panels (19) overlying said network, each of said panels being an aluminum extrusion;

(E) heating means (50) inside each of said panels;

(F) means (52) for electrically connecting said elements to a power source; and

(G) wherein an end of said first-mentioned tube (16) is secured to said landing so that each said tread surface is substantially horizontal.

19. An improved stairway construction as defined in claim 18 wherein (A) each said heating element is an electrical tape; and

(B) further including heat insulating material (54) containing inside each said panel below said heating element, said insulating material functioning also as a sound dampener to eliminate rings or echoes within each said panel.

20. An improved stairway construction comprising (A) an elongated tube (16) for connection to a stairway landing (12);

(B) one or more shell-like steps (14) arranged crosswise on said tube, each said step having an anodized tread surface (14a);

(C) means (78) for anchoring each of said steps to said tube;

(D) a landing (12), said landing comprising 1) tubes (17) secured together to form a framing network; and

(2) one or more matched panels (19) overlying said network, each of said panels and tubes being hollow aluminum extrusions; and

(3) wherein an end of said first-mentioned tube (16) is secured to said landing so that each said tread surface is substantially horizontal.

21. An improved step for an open-riser stairway comprising (A) an open, downwardly-dished aluminum shell (32),

said shell having a flat rear wall (40) for engagement with a stringer;

(B) a relatively flat aluminum cover (30) engaging over said shell to close it, said cover (1) constituting an anodized tread surface of said step; and

(2) making an acute included angle with said rear Wall;

(C) an electrical heating element (50) fastened to the inside of said cover just below said tread surface; (D) a connector (52) protruding from said step for electrically connecting said heating element to a power source; and

-' (E) a material selected from the group consisting of graphite and glycerine impregnating said tread surface.

-22.-An' improved step for an open-riser stairway as defined in claim 21 wherein (A) said heating element is an electrical tape; and

a (B) further including thermal insulating material (54) contained inside said step below said heating element.

23;An improved step for an open-riser stairway as defined in claim 21 and further including (A) a hollow triangular reinforcement (56) nested inside one end of said step adjacent said cover for anchoring a railing support to said step; and (B) means (57) for fastening said reinforcement to saidstep. 24. An improved step for an open-riser stairway comprising (A) an open, downwardly-dished shell (32), said shell having (1) a flat rear wall (40) for engagement with a stringer; and I (2) relatively flat side walls (36) which splay out to the opposite ends of said shell and constitute supporting struts; (B) a relatively flat cover (30) engaging over said shell to close it, said cover (I) constituting the tread surface of said step; (2) making an acute included angle with said rear wall; and (3) having a slight camber; and (C) wherein step is generally trapezoidal.

25. An improved step for an open-riser stairway comprising (A) an open, downwardly-dished shell (32), said shell having a flat rear wall (40) for engagement with a stringer; 10 (B) a relatively flat cover (30) engaging over said shell to close it, said cover (1) constituting the tread surface of said step;

and (2) making an acute included angle with said 15 rear wall (C) an electrical heating element (50) inside said step just below said cover; and (D) a connector (52) protruding from said step for electrically connecting said heating element to a 20 power source. I

References Cited UNITED STATES PATENTS 1,349,136 8/1920 Lillard. 5 2,479,736 8/1949 Fieroh 182-106 2,749,188 6/1956 Mitchell 182-83 FOREIGN PATENTS 1,028,341 5/1966 Great Britain.

U.S. Cl. X.R. 

